The present invention relates to a method of transmitting and receiving signals by a serial-digital-interface system employed in a broadcasting studio, and a transmitter and a receiver in the same system.
Various types of serial-digital-interface systems (hereinafter referred to as SDI system) are employed in studios of a broadcasting station. The SDI systems serialize digital video signals in various formats, then transmit the signals between video-editing devices used in the studios, thus the SDI systems must be compatible with respective formats of video signals. The Society of Motion Picture and Television Engineers (SMPTE) and The Association of Radio-wave Industrial Business (ARIB) standardized SMPTE259M standard, SMPTE292M standard, and BTA S-004B standard and so on. Those standards specify formats of serializing digital-video-signals of various formats in parallel form. The xe2x80x9cSCOPES OF SMPTE STANDARDxe2x80x9d describes that SMPTE259M standard specifies an SDI of 10-bit (4:2:2) component signal operating at 270 Mbps, and SMPTE292M standard specifies an SDI operating at approx. 1.5 Gbps for component signals of High-Definition-Television (HDTV).
Those standards tell that numbers of source formats differing in the following items are used in broadcasting stations: frame frequency, a number of active scanning lines, a number of pixels per frame, scanning method (interlace, progressive methods). For instance, the video signals in such various formats follows are available in the studios:
Standard Definition Television (SDTV) signal:
scanning-lines; 525
frame frequency: 30/1.001 Hz
scanning method: interlace 480/60 I (hereinafter referred to as 480/60 I)
SDTV signal:
scanning-lines; 525
active lines: 487
frame frequency: 60/1.001 Hz
scanning method: progressive 480/60 P (480/60 P)
HDTV signal:
scanning-lines; 1125
active lines: 1080
frame frequency: (30/M) Hz
scanning method: interlace 1080/60 I
HDTV signal:
scanning-lines; 1125
active lines: 1035
frame frequency: (30/M) Hz
scanning method: interlace 1035/60 I
HDTV signal:
scanning-lines; 750
active lines: 720
frame frequency: (60/M) Hz
scanning method: progressive 720/60 P
where M represents 1 or 1.001.
When one of the STDV video signals, i.e. a signal of 480/60 I method, is serialized and transmitted in accordance with the SMPTE259M standard which is one of SDIs for the SDTV, the signal undergoes the following processes. FIG. 2 illustrates a sampling structure per frame of the video signal by 480/60 I system. The format of this video signal is as follows: frame frequency=30/1.001 Hz, a number of scanning lines=525, a number of samples (words) per scanning line =858, a number of active samples (words)=720, a sampling frequency=13.5 MHz. This luminance signal and two color-difference signals are sampled at one half the frequency of luminance signal, and then multiplexed to form a multiplexed color signal. This multiplexed color signal, is multiplexed to the luminance signal in each word, then transmitted at 270 Mbps.
On the other hand, when one of HDTV signals, i.e. a video signal of 1080/60 I method, is serialized and then transmitted in accordance with the SMPTE292M standard, or BTA S-004 standard which is one of SDIs for the HDTV, the signal undergoes the following processes. The format of this video signal is as follows: frame frequency=30/1.001 Hz, a number of scanning lines=1125 (1080 active), a number of samples (words) per scanning line=2200, a number of active samples (words)=1920, a sampling frequency=74.25/1.001 MHz. The luminance signal and color-difference signals are structured in the same way as discussed above. The luminance signal and color difference signals are multiplexed to each word, then transmitted at 1.485/1.001 Gbps.
FIG. 25 illustrates a structure of a conventional SDI system compatible both with the HDTV and SDTV. This SDI system comprises transmitter 309 and receiver 315. In transmitter 309, parallel-video-data (video signal (1) in FIG. 25) in HDTV, 1080/60 I format and another parallel-video-data (video signal (2) in FIG. 25) in SDTV, xe2x80x98480/60 Ixe2x80x99 format comprises luminance signals (hereinafter referred to as Y-signal) in 10-bit, and multiplexed color-difference signals (hereinafter referred to as C-signal). This parallel-video-data are fed into HD interface formatting circuit 306 and SD interface formatting circuit 326 respectively in 20-bit parallel form. In these formatting circuits 306 and 326, an end of active video (EAV) signal as well as a start of active video (SAV) signal is multiplexed to respective Y and C signals. The EAV signal is a timing-reference signal indicating an end of horizontal and vertical active periods, while the SAV signal is a timing-reference signal indicating a start thereof. Line number data and an error-detecting-code are also multiplexed to Y and C signals in formatting circuit 306, and they are supplied as an interface format. Output from interface formatting circuits 306 and 326 are fed into parallel to serial converting circuits (hereinafter referred to as a P/S converting circuit) 307 and 327, where the least significant bit (LSB) of C-signal and onward including C-signal and Y-signal in this order undergo the P/S conversion and then they are output to scrambling circuits 308 and 328. Circuits 308 and 328 scramble the input signals with generating function (X9+X4+1) (X+1), and output them. The signals scrambled in circuit 308 are converted into voltages in accordance with the SMPTE292M standard by a voltage-converting-circuit (not shown), and are output as a serial signal. A transmitting speed of the HDTV signal output here is approx. 1.5 Gbps. The signal scrambled in circuit 328 is converted into a voltage in accordance with the SMPTE259M standard, and output as a serial signal. A transmitting speed of the SDTV signal output here is approx. 270 Mbps.
Those signals are fed into receiver 315, where waveform-equalizing circuits 310 and 330 receive the serial signals of HDTV and SDTV from transmitter 309. Circuits 310 and 330 compensate degraded signals due to a coaxial cable used in the transmission line, and equalize the waveforms thereof then output the signals. Clock reproducing circuits 311 and 331 receive the output from waveform-equalizing-circuits 310 and 330, extract clock component thereby reproducing a clock signal, then output serial data and serial clock signal. De-scrambling circuits 312 and 332 receive the serial data as well as the serial clock signal from circuits 311 and 331, and then descramble and output them. Serial to parallel converting circuits (S/P converting circuit) 313 and 333 receive the serial data descrambled, and convert the data into parallel form, then output the parallel data. HD interface deformatting circuit 314 and SD interface deformatting circuit 334 receive the parallel data from circuits 313 and 333, and convert them into video-parallel-data in the same format as the signals have been fed into transmitter 309, then output the data. As discussed above, respective SDI systems for SDTV and HDTV are prepared independently, and thus each type of signals employs respective appropriate systems.
If various video formats, e.g. HDTV and SDTV, can be transmitted through an identical SDI system and an identical transmission line, and further if the SDI system can transmit a plurality of channels, it will produce great advantages in this industry. The advantages include, (a) reducing a number of transmission lines, (b) simplifying the work of preparing the transmission lines, (c) downsizing the circuit of SDI system, and (d) reducing the cost of SDI system. However, when the various formats discussed above are serialized, transmission speed thereof may be 270 Mbps for SDTV, 480/60 I format, and 540 Mbps for SDTV, 480/60 P format (for instance, 270 Mbps through two lines). On the other hand, serialized HDTV format produce the transmission speed of 1.485/1.001 Gbps, or 1.485 Gbps. Since these two speeds has only a small difference, a transmitter and a receiver compatible with these two speed can be realized with ease. However, the difference in transmission speed between SDTV format and the HDTV format, i.e. 270 Mbps, 540 Mbps and 1.485 Gbps, 1.485 /1.001 Gbps is great, and also both the formats uses different multiplex-methods of digital sync signal at serializing. As a result, it has been difficult to realize a common transceiver compatible with both of the format. In the SDI system, the transmitter sometimes produces a sequence of specific identical codes at outputting serial data depending on a level of parallel video data fed into the transmitter. The receiver in the system needs a waveform equalizing circuit for compensating a signal degraded through a coaxial cable used in the transmission line and a clock-signal-reproducing-circuit for reproducing a serial clock signal from the serial data.
When the identical code is sequentially fed into the receiver, the waveform equalizing circuit has a difficulty to identify the post-equalizing. digital values, i.e. xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d, because low frequency component is cut off in the equalizing circuit. This situation may produce errors. Further, in the clock-signal-reproducing-circuit, the clock-signal component to be extracted becomes less. This situation thus may produce errors. The problem of the identical code occurring sequentially is discussed in xe2x80x9cPathological Check Codes for Serial Digital Interface Systemsxe2x80x9d published from SMPTE Journal, August 1992, page 553-558. Patterns of a sequence of specific and identical code are shown in FIG. 24. FIG. 24(A) shows a pattern where a sequence of 20-bit stands at xe2x80x9c1xe2x80x9d and the next sequence of 20-bit stands at xe2x80x9c0xe2x80x9d. FIG. 24(B) shows a pattern where the first one bit stands at xe2x80x9c1xe2x80x9d followed by 19-bit standing at xe2x80x9c0xe2x80x9d. Another pattern where the order is reversed is available, i.e. the first bit stands at xe2x80x9c0xe2x80x9d followed by 19-bit standing at xe2x80x9c1xe2x80x9d. These patterns are called pathological pattern, which may be produced when the same scrambling circuit that in the SDI system is used. When parallel-video-data fed into the receiver produces specific two values in sequence, these patterns may occur in the output from the transmitter. These specific values are described in the document introduced above.
Parallel-video-data is multiplexed with timing-reference-signals of EAV and SAV. These reference signals include the words of 3FFh, 000h, 000h indicating the end and the start of active video period. These values are not included in the specific values discussed above. Therefore, when the EAV or SAV is fed into the parallel-video-data, the sequential production of identical codes stops even if one of the patterns shown in FIG. 24 occurs in sequence.
As a result, the maximum length of the sequence of that specific value is an active video period from the SAV to EAV. An active video period per line of an HDTV signal is 1920 words for Y and C signals respectively. The SDI system accommodating the HDTV format now commercialized is equipped with a receiving circuit which works properly within the active video period, i.e. up to 1920 words.
It can be considered that a plurality of channels of SDTV signals which has less data are multiplexed for transmitting the signals at a transmission speed of the serial data in the HDTV format. However, when the plurality of channels of SDTV signals are multiplexed, the number of multiplexed words to be transmitted may exceed 1920 words, i.e. an active video period of the HDTV format. As such, when the SDTV signal is transmitted through the SDI of the HDTV format, and received by the same waveform equalizing circuit as well as clock reproducing circuit as those in the SDI at receiver side of the HDTV format, the maximum length (i.e. the active video period) of producing an identical code in series is longer than that in the HDTV case. This situation thus may produce errors. Therefore, when the multiplex of plural SDTV signal causes the active video period to exceed 1920 words, it is not proper for the signals to be transmitted through the hardware of the SDI for the HDTV format.
The present invention aims to transmit a video signal in the SDTV format through an interface for a serial digital signal in the HDTV format. A transmission method of the present invention allows video signals in the SDTV format of at least one channel to be transmitted as HDTV signals through one channel, or allows video signals in the SDTV format of N channels (N is integer not less than one.) to be transmitted in a serial-digital form. A total number of bits of luminance signal (Y-signal) to be transmitted within one frame of an HDTV signal is divided into units corresponding to a total number (K) of scanning lines per frame of SDTV signal of one channel for producing K units to be transmitted. Among these K units, two series of signals comprising K units per frame are formed in the units corresponding to active scanning lines. This signal in the two series includes at least the following elements:
(a) predetermined control signal word;
(b) a signal comprising samples containing xe2x80x9cNxc3x97a number of words of Y-signalxe2x80x9d in a predetermined period within one horizontal scanning period of the SDTV; and
(c) a word corresponding to a predetermined level.
These two series of signals are serialized, then transmitted in a single series.
The present invention further aims to provide a transmitter which carries out the transmission method discussed above.
Still further, the present invention aims to provide a receiving method and a receiver which automatically detect a format transmitted through the interface discussed above using a digital sync, signal and a line number.